Origins of the 405 line system.

[ppppenguin]

Lift and syncs were added to the waveform very late in the M-EMI processing chain.  I assume that the intention was to give the black-level clamps as much black level as possible to work on.

Also why bother to add syncs early in the chain if they are going to be replaced later. If you need to feed a signal without syncs to a monitor then just use external sync. All this matters a lot more with valves than transistors. You really don't want to use more valves than you really need to do the job.

Gryphon also raises the old question of lift, or pedestal. I think the 405 system acquired and lost pedestal more than once in its life, ending up without it. The 525 line US system had it from the start and kept it until the end of NTSC. Except for the Japanese variant. In modern terms it's a nuisance and also wastes transmitter power. So why was it used at all? Presumably to help the poor or non-existant flyback blanking in many TVs.

Coming back to the crossfade. If you can do a crossfade you can do a cut, simply by doing it faster. From experience of designing vision mixers I know that doing a decent crossfade is a far more complex business than a simple cut. In the simplest system you can cut directly on push button switches or relays. It's hardly elegant and will put a glitch in the picture but it works. Perhaps EMI (this is definitely the EMI end of things, not Marconi) hadn't developed a reliable interfield cut system and a mix eliminated the problem. Seems a bit unlikely since they had, for the period, very sophisticated circuit techniques.